Abstract
Activation of unfolded protein response (UPR) has recently been identified as a new target for cancer therapy. However, pharmacological agents activating UPR have not been approved in clinical practice. In this study, spatiotemporally controllable UPR activation was realized by the combination of ultrasound (US)-triggered sonodynamic therapy (SDT) with titanium nitride (TiN) NPs and proteasome inhibitor bortezomib (BTZ). BTZ-conjugated TiN NPs were prepared by using a linker of carminic acid (CA)-functionalized bovine serum albumin (BSA). CA interacts with BTZ to form dynamic boronate ester bond enabling pH- and ultrasound-responsive drug release and thus overcoming the challenge of poor drug release for the conventional delivery systems. Compared with traditional sonosensitizer TiO(2), TiN has superior SDT efficiency. TiN-mediated SDT inhibits not only the β1/β5 active sites of proteasomes, but also the β2 proteasome activity not targeted by BTZ, thus synergistically triggering endoplasmic reticulum (ER) stress. Moreover, SDT and BTZ complement each other perfectly to activate all three pro-apoptotic UPR pathways including PERK/eIF2α/ATF4, IRE1/JNK and ATF6, thereby leading to dramatic upregulation of CHOP expression, calcium overload and mitochondrial dysfunction. Importantly, this intensified ER stress effectively triggers immunogenic cell death (ICD), characterized by the massive release of damage-associated molecular patterns (DAMPs), thereby further recruiting and activating cytotoxic T lymphocytes and reshaping the immunosuppressive tumor microenvironment. In summary, making up the current lack of effective pharmacological agents activating UPR, this study provides a new strategy to spatiotemporally activate UPR through the ingenious combination of SDT and proteasome inhibition with BTZ-conjugated TiN NPs.